访问 shared_ptr 数组

Question

#include <memory>

int main()
{
   std::shared_ptr<double> array (new double [256], [](double * d){
      delete [] d;
   });
}

I made a shared_ptr pointing into an array of doubles which has its own custom deleter.

Now how can I access the array? Let's say I wish to access the array at index 1 . I tried the usual "bracket method" but I get errors.

The word array points to its first element by default, but what if I want to access the 2nd element? Using increments and bracket gives me the "no match for operator" error.

Can someone explain to me what's happening under the hood?

I am asking this for research purposes, despite being aware that unique_ptr and vector will do a better job.

Answer 1

The bracket notation is defined to work with pointer types (and you're right that, given array array , the expression array decays to an expression with such a type which points to the first element) but, despite its function, std::shared_ptr is not a pointer type .

You would have to obtain the raw pointer first :

array.get()[n];

Where n is, of course, a valid array subscript.

This is also the case with std::unique_ptr (though note that, in that case, you do not need to supply your own deleter! ).

Answer 2

in C++17, support for array of shared_ptr like in unique_ptr( c++11).

int main()
{

   std::shared_ptr<double[]> array1 (new double [3]{4,5,6}, [](double * d){
   delete [] d;});

   std::unique_ptr<double[]> array2 (new double [3]{4,5,6}, [](double * d){
   delete [] d });
}